We prpose to isolate mutant S49 lymphoma cells with lesions affecting hormone-sensitive adenylate cyclase, and to use the mutant phenotypes to elucidate the molecular basis of hormone action in membranes of animal cells. Mutant clones will be selected from chemically mutagenized S49 population by virtue of their resistance to the killing action of stimulators of adenylate cyclase, such as cholera toxin and beta-adrenergic amines. New mutant phenotypes will be selected and distinguished from already described phenotypes by means of: 1. Screening multiple clones for cyclase stimulation by drugs; 2. Testing clones for their ability to complement already isolated phenotypes in somatic hybrids; 3. Selection of revertants and partial revertants from mutants already isolated and described. Hormone-sensitive adenylate cyclase in membranes of these mutants will be biochemically compared with previously isolated mutants with respect to receptor-cyclase coupling and guanine nucleotide regulation. We will also use new phenotypes to develop in vitro complementation assays as a means of identifying undefined components of adenylate cyclase. Finally, we plan to isolate and biochemically characterize clones bearing lesions that affect agonist-induced refractoriness to beta-adrenergic agonists, in an attempt to understand the biochemical basis of this adaptive response to hormonal stimulation.